Such radiation-emitting semiconductor diodes, especially if the wavelength of the emission is in the visible part of the spectrum, are suitable radiation sources--if designed as diode lasers--for inter alia information-processing systems such as laser printers with which information is written, optical disc systems such as Compact Disc (Video) (CD(V)) players or bar code readers, by which information is read, and Digital Optical Recording (DOR) systems, by which information is written and read. There are also numerous applications in optoelectronic systems for LED versions of such diodes.
Such a radiation-emitting diode and such a method for manufacturing same are known from the article "AlGaInP Double Heterostructure Visible-Light Laser Diodes with AlGaInP Active Layer Grown by Metalorganic Vapor Phase Epitaxy" by K. Kobayashi et al., published in IEEE Journal of Quantum Electronics, vol. QE-23, no. 6, June 1987, p. 704. In this article, a radiation-emitting semiconductor diode is described on which an active layer of InGaP is present on a substrate of n-GaAs between two cladding layers of InAlGaP. The semiconductor materials of these layers each comprise a mixed crystal having two sublattices in which the phosphorus atoms are present on the one sublattice and the atoms of the other elements, in this case In and Ga atoms for the active layer and In, Al, and Ga atoms for the cladding layers, are present on the other sublattice. A buffer layer of GaAs is present between the substrate and the first cladding layer. The wavelength of the emission of the diode, which is constructed as a laser here, is approximately 670 nm (i.e. the wavelength in photoluminescence is approximately 660 nm, which corresponds to a band gap of approximately 1,88 eV).
A disadvantage of the known radiation-emitting semiconductor diode is that the experimentally found wavelength for the emission is higher than the theoretically expected one: for example, the wavelength expected for an InGaP active layer is approximately 650 nm, whereas approximately 670 nm or more is often found in practice. A similar effect occurs in the case of cladding layers comprising InGaAlP, where the experimentally found band gap again is less than the theoretically expected one. The band gap of both the active layer and the cladding layer may be increased by increasing the aluminum content of these layers. This possibility is limited, especially for the cladding layers which contain indirect semiconductor materials, because progressive addition of aluminum results in an ever smaller increase in the band gap, and doping of the cladding layers becomes more difficult. As regards the active layer, another possibility is to make the latter thinner, which, however, renders manufacture more difficult. It was found experimentally that the use of misoriented substrates, for example (311) or (511) substrates, causes the experimental band gap--and thus the wavelength of the emission--to lie (much) closer to the theoretically expected value. The use of misoriented substrates, however, is more expensive and has the drawback that it restricts the choice of the longitudinal direction of the resonance cavity.